1. Field of the Invention
The present invention relates to a solid-state image pickup element in which signal charges are transferred by CCDs and an image pickup apparatus using the same.
2. Description of the Related Art
In the related art, as a solid-state image pickup element in which a color filter is not used, a stack-type solid-state image pickup element disclosed in, for example, JP-A-2002-83946 has been proposed. The stack-type solid-state image pickup element has a configuration where photoelectric converting films made of three organic materials which respectively detect red (R) light, green (G) light, and blue (B) light are stacked above a semiconductor substrate, signal charges generated in the films are accumulated in accumulation diodes formed on the semiconductor substrate, and the signal charges accumulated in the accumulation diodes are read out by a signal read circuit such as vertical CCDs and a horizontal CCD, and then transferred. In such a stack-type solid-state image pickup element, the utilization efficiency of light can be improved, and a false color can be suppressed, so that a color image of high quality can be produced.
The stack-type solid-state image pickup element requires a contact conductor through which one of two electrodes sandwiching each of the photoelectric converting films stacked above the semiconductor substrate is connected to each of the accumulation diodes formed on the semiconductor substrate. The material of the contact conductor is a metal such as tungsten, copper, or molybdenum, and a high temperature of 300 degrees or higher is necessary in formation of the conductor structure. On the other hand, the photoelectric converting films stacked above the semiconductor substrate are made of organic materials, and hence their performance is obviously impaired when exposed to a high temperature of 200 degrees or higher. In the stack-type solid-state image pickup element, for example, a production step of forming a contact conductor and then forming one of the photoelectric converting elements is repeated three times. Consequently, there is a problem that the performance of the photoelectric converting element which has been previously formed is impaired by the temperature of the formation of the contact conductor.
As a solid-state image pickup element which can solve the problem, a hybrid element has been proposed in which photoelectric converting elements detecting R and B and made of silicon are integrated on a semiconductor substrate, and one photoelectric converting film detecting G and made of an organic material is stacked above the semiconductor substrate (for example, see JP-A-2003-332551 (Paragraph 0035)). In the hybrid solid-state image pickup element, since the performance of silicon is not impaired even at a high temperature of 300 degrees or higher, the lower portion (the photoelectric converting elements and contact conductors) can be previously formed by a high-temperature process, and then the photoelectric converting film can be formed by a low-temperature process. Therefore, the performance of the photoelectric converting film can be prevented from being impaired.
In the hybrid solid-state image pickup element, the light-receiving area of the photoelectric converting film in the upper portion can be increased, and the aperture ratio of the photoelectric converting film in the upper portion can be set to approximately 100%. Therefore, the amount of signal charges generated in the photoelectric converting film can be increased. Furthermore, the area of the accumulation diode disposed in the lower portion can be made smaller, and hence the sizes of the photoelectric converting elements can be increased. Therefore, the amount of signal charges accumulated in the photoelectric converting elements can be increased.
Since the amount of signal charges is increased, color image data of high quality can be produced. When a CCD is used as a signal read circuit, however, a signal charge transfer capacity sufficient for the increased amount of signal charges is required.